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: 



A MANUAL 
OP SOIL PHYSICS 






BY 



PERCY Bj BARKER, M.A. 

PROFESSOR OF AGRONOMY IN THE UNIVERSITY OF NEBRASKA 



AN J) 



HORACE J. YOUNG, B.Sc. 

ASSISTANT PROFESSOR OF AGRONOMY IN THE UNIVERSITY OF NEBRASKA 



GINN AND COMPANY 

BOSTON • NEW YORK • CHICAGO • LONDON 
ATLANTA • DALLAS - COLUMBUS • SAN FRANCISCO 



S52A 



<§* ft- 



COPYRIGHT, 1915, BY 
PERCY B. BARKER AND HORACE J. YOUNG 



ALL RIGHTS RESERVED 
315.9 



<$0; 



uC 



G1NN AND COMPANY- PRO- 
PRIETORS • BOSTON • U.S.A. 



©CI.A416192 

m -2 1915 



PREFACE 

The exercises described on the following pages are intended to 
give the student an understanding of the origin, composition, and 
physical properties of soils and to show the relations of these 
properties to methods of soil management. The work outlined in 
the manual is sufficient for two semestprs, but may be completed 
in less time if more than two laboratory periods are held per week. 

While these exercises are the outcome of ten years' experience 
in teaching the important physical properties of soils, they are 
not all original with the authors. Material has been drawn from 
many sources and arranged to give the best applications to 
important principles of soil management. 

In connection with each exercise, references have been given 
and questions asked. It is hoped that this method of study will 
enable the student to obtain a great amount of information 
relative to the application of each exercise. 

THE AUTHORS 

University of Nebraska, College of Agriculture 
Lincoln, Nebraska 



[iii] 



3. 



CONTENTS 

PAGE 

Introduction 1 

KXERCISE 

I. A Study of Soils in the Field 3 

II. Soil Kegions and Precipitation 5 

III. Geological Map and Vertical Section of State . . 7 

IV. Soil Classification 9 

V. Examination of Soil Particles 11 

VI. Soil-forming Minerals 13 

VII. Soil-forming Rocks 15 

VIII. Volume Density and Porosity 17 

IX. Number and Surface Area of Soil Particles ... 21 

X. Flow of Air through Soils 23 

XI. Percolation of Water 25 

XII. Determination of Hygroscopic Moisture .... 27 

XIII. Capillary Rise of Water in Soils 29 

XIV. Effect of Organic Matter and Dry Clods upon 

Capillarity 33 

XV. Power of Soils to retain Water against Percolation 35 

XVI. The Effectiveness of Mulches 39 

XVII. Effect of Water upon Soil Volume 43 

XVIII. Loss on Ignition 45 

XIX. Soil Acidity and Basicity 47 

XX Determination of Humus 49 

XXI. Leaching of Soils 51 

XXII. Power of Soils to absorb Salts 53 

XXIII. Absorption of Gases by Soils 55 

XXIV. Absorption of Moisture by Soils 57 

XXV. Flocculation of Clay 59 

XXVI. Effect of Lime on Soil Structure ....... 61 

[v] 



MANUAL OF SOIL PHYSICS 

EXERCISE PAGE 

XXVII. Effect of Sand and Organic Matter on Soil 

Structure 63 

XXVIII. Effect of Alternate Wetting and Drying on Soil 

Structure 65 

XXIX. Effect of Alternate Freezing and Thawing on 

Soil Structure 67 

XXX. Effect of Color on Soil Temperature .... 69 

XXXI. Effect of Water on Soil Temperature .... 71 
XXXII. Effect of Vegetation and Topography <>n Soil 

Temperature 73 

XXXIII. Effect of Cultivation on Soil Temperature . . 75 

XXXIV. Soil Tenacity 77 

XXXV. Transference of Heat in Soils 79 

XXXVI. Absolute Specific Gravity of Soil 81 

XXXVII. Apparent Specific Gravity of Field Soils . . 83 

XXXVIII. Specific Heat of Soils 85 

XXXIX. Evaporation of Water 87 

XL. Moisture Determinations of Field Soils . . 89 

XLI. Standardization of the Eyepiece Micrometer . 91 

XLII. Mechanical Analysis of Soils 93 

XLIII. Soil Examination 97 

XLIV. Examination of Soil Samples 99 

Weights and Measures 101 



«•< 



[vi] 



MANUAL OF SOIL PHYSICS 



INTRODUCTION 
SOIL SAMPLING 

In collecting samples of soil for study in the laboratory, 
great care should be taken to obtain samples that are repre- 
sentative of the soils in the area from which they are taken. 
Avoid taking samples in places where conditions are unusual, 
such as gopher mounds, squirrel holes, footpaths, cattle trails, 
old roadways, depressions, and other places showing abnormal 
plant growth. 

After selecting a place which represents the soil and field 
conditions, scrape away from the surface all foreign matter 
and plant remains. The underground parts of plants, as well 
as insects and other animal life in the soil, are considered as 
a part of it. 

The tools commonly used in taking samples are augers and 
soil tubes (Fig. 14). In sampling by the auger method, two 
augers, one 3 and one 6 feet long, are usually employed. By 
using a smaller bit on the 6-foot auger, samples may be 
procured which are less contaminated with soil from the 
upper three feet. Marks are made upon the shanks of the 
augers so that the depth from which the sample is being 
taken may be easily ascertained. The soil obtained from each 
foot is placed in a separate bag or container and labeled ac- 
curately as to the location and depth. After the sample from 
one foot has been obtained, work the auger up and down in 
the hole several times and discard the soil which sticks to the 

[1] 



MANUAL OF SOIL PHYSICS 

bit. This helps to keep the soil from the next foot from being 
contaminated with that above. In this manner continue the 
sampling to the desired depth. 

The soil tube has a cutting edge somewhat smaller than 
the bore. It is simply driven into the soil to the depth of 
one foot at a time, and a core of soil taken throughout the 
foot. For convenience, two or more tubes of different lengths 
are used. 

If the samples are being taken for determining the total 
moisture in the field, precautious should be taken to prevent 
evaporation. For this purpose tight metal boxes or glass jars 
are usually employed. 

The making of detailed studies of the soil sometimes calls 
for inch samples. A convenient method of procuring Buch 
samples is by means of the Nebraska Soil Anger < Fig. 13). 
This auger is also useful in obtaining a known volume of soil 
for determining the apparent specific gravity and porosity of 
field soil. 

Since the composition and physical characters of soils of the 
same type (especially soils of glacial origin) vary somewhat, 
it is the practice to take what is known as a composite sample. 
This means the taking of several samples in the same type 
and uniting them. The larger the number of places from 
which soil is taken, the more representative the sample. A 
composite sample made up of soils from three different loca- 
tions will usually be fairly representative of areas of less than 
ten acres. 



[2] 



EXERCISE I 

A STUDY OF SOILS IN THE FIELD 

Object. The object of the exercise is to make a thorough 
study of soils under field conditions. 

Materials needed. Four-foot auger; 6-foot auger; drawing 
paper ; notebook. 

Procedure. Examine several types of soil to the depth of 
6 feet, with special reference to the following points: 

1. Depth of the surface soil at different locations. 

2. Texture and structure at different depths. 

3. Amount and distribution of the organic matter at vari- 
ous depths and locations. 

4. Variations in color. 

The soil types should be selected so as to give a variation 
in the depth of the surface soil and in the topography. In 
each type ascertain accurately the depth of the surface soil. 

Describe each of the soil types examined, giving due em- 
phasis to depth of surface soil, distribution and amount of 
organic matter, texture, structure, color, and topographic 
effects. Draw a section of each type examined, using a scale 
of 1 inch to the foot, showing the depth of the surface soil, 
the location of lime concretions, etc. In drawing the sections, 
use the following legend : 







li! 






■HI 




WiMiWiiiii 







Subsoil Hard-pan (gumbo) Lime concretions Iron concretions 

Fig. 1. Legend used in drawing sections 

[3] 



MANUAL OF SOIL PHYSICS 
References : 

Widtsoe : Dry-Farming, pp. 59-73. 

Wiley: Principles and Practices of Agricultural Analysis, Vol. I, 

pp. 59-60. 
Hilgard : Soils, pp. 120-187. 
Lyon and Fippin : Soils, pp. 68-69. 

Questions : 

1. State briefly what is understood by the following terms : 

(a) surface soil; (b) subsoil. 

2. Explain briefly (a) the difference between the surface soil 

in arid and in humid regions ; (ft) the difference between 
the subsoil in arid and in humid regions. 

3. Account in as many ways as possible for the even distri- 

bution of the organic matter in the surface soil. 



*- 






[4] 



EXERCISE II 

SOIL REGIONS AND PRECIPITATION 

Object. The object of the exercise is to make a study of 
the soil regions of the state or county, together with the 
distribution of rainfall. 

Materials needed. Ruler; hard pencil; base map of state 
or county ; guide map. 

Procedure. Draw upon the base map all the regions of main 
types of soil indicated on the guide map, and the lines repre- 
senting the annual precipitation. Use the same legend as has 
been used on the guide map ; also place this legend at the 
bottom of the map. 

References : 

Condra : Geography of Nebraska, pp. 72-113. 

Annual Report of the Nebraska Slate Board of Agriculture (1909), 

pp. 271-311 
In other states the experiment station bulletins and the sxirveys of 

the United States Bureau of Soils will give valuable information. 

Questions : 

1. How many square miles are there in each region ? 

2. What is the origin of the soil in each region : (a) residual ? 

(b) glacial? (c) loess? (d) alluvial? 

3. What is the average annual precipitation in the state or 

county ? 

4. In which soil region is your home farm located ? 

5. What is the annual precipitation on your home farm ? 

6. Name two crops that are profitably raised in each soil region. 

[5] 



t 



, 



EXERCISE III 

GEOLOGICAL MAP AND VERTICAL SECTION <>K STATE 

Object. The objecl of the exercise is to make si study of 
the Important geologic formations of the state, with reference 
to their part in soil making. 

Materials needed. Ruler; hard pencil; base map of state 
or county; drawing paper ; guide maps. 

Procedure. Draw a map of the State <>r county, showing 
the geologic formations as they are exposed <>n the surface. 
Usr the same legend as is used on i\w guide map; also place 
the Legend in the margin of the map. Draw, according to scale, 
b vertical-section profile map, showing the underlying forma- 
tions of the state or oounty. Label each formation carefully. 

References : 

Annual Report of the Nebraska State Board of Agric.uUurc (l'.xxs 

L907), pp. 826 844. 
The bulletins of the State Agricultural Experiment Station or 
of the State Geological Survey will give valuable Information 
for this exercise. 

Questions : 

1. N aim* in order, commencing with the oldest exposed, all the 

underlying Formations In the state or oounty. 

2. What is the surface geologic formation of y borne farm? 

:i. How many formations underlie your home farm hi- place? 

NTame them. 
I. \\ iiiiii formations give rise to good productive .soils? 
5. W'IihIi formations furnish a good watei supply? Which a 

poor water supply ? 

[7] 



c- 



EXERCISE IV 
SOIL CLASSIFICATION 

Object. The object of the exercise is to become familiar, 
first, with the different soil types, and, second, with the scheme 
of soil classification. 

Materials needed. Three-foot auger; notebook. 

Procedure : 



Classification as to 
Origin 




Physical Classification 


1. Sedentary 
a. Residual 


1. 

2. 


Structure 


Class 


b. Cumulose 


3. 


Organic matter 




2. Transported 
a. Colluvial 


4. 
5. 


Origin 
Color 




b. Water 

(1) Marine 

(2) Lacustrine 

(3) Alluvial 

3. Glacial 

4. iEolian 


6. 

7. 

8. 

9. 

10. 


Depth 

Drainage 

Topography 

Native vegetation 

Natural productiveness 


. Series 



Type 



The field selected for study should contain as many differ- 
ent soil types as can be found together. In this exercise the 
following points must be kept in mind: texture, structure, 
organic matter, origin, color, depth, drainage, topography, 
native vegetation, and natural productiveness. Also the 
meaning of the following terms should be well understood: 
soil province, soil series, soil class, and soil type. 

[9] 



MANUAL OF SOIL PHYSICS 

Write a full description of each soil type that you have 
studied, giving due emphasis to the ten points mentioned 
above. 

References : 

Lyon and Fippin : Soils, pp. 69-80. 

Hopkins: Soil Fertility and Permanent Agriculture, pp. 114-136. 

" Soils of the United States," in Bulletin No. 96 of the United States 
Department of Agriculture, Bureau of Soils, pp. 109-165, SOS- 
SSI, 465-495. 

Questions : 

1. What is understood by a soil province, soil series, soil class, 

and soil type ? Give one example of each. 

2. Describe the following classes of soils as used by the 

United States Bureau of Soils : («) fine sandy loam ; 
(b) silt loam ; (c) loam ; (<7) clay loam ; (e) clay. 

3. How deep are soils sampled in establishing soil types ? 



[10] 



EXERCISE V 

EXAMINATION OF SOIL PARTICLES 

Object. The object of the exercise is to study soil particles, 
with and without the microscope, in order to become familiar 
with the general composition of soils. 

Materials needed. Microscope ; sand ; surface soil ; subsoil ; 
clay ; drawing paper ; pen or hard pencil. 

Procedure. Examine, without the aid of the microscope, a 
small amount of sand, noting the color and adhesion of the 
particles. Examine a small amount of sand with the micro- 
scope, noting the color, shape of the particles, and any cohe- 
sion. While the mount of sand is under the microscope, make 
a drawing of several particles to show their comparative sizes 
and shapes. 

In the same manner examine some of the surface soil, the 
subsoil, and the clay, placing the drawings on the same piece 
of paper with the drawings of the sand particles. In studying 
the surface soil, note the structure of the crumbs, comparing 
it with the same structure in the subsoil and in the clay. 

References : 

Snyder : Soils and Fertilizers, pp. 11-20, 326. 

Lyon and Fippin : Soils, pp. 69-79. 

Wiley : Principles and Practices of Agricultural Analysis, Vol. I, 

pp. 282-290. 
"The Mineral Composition of Soil Particles," in Bulletin No. 54 

of the United States Department of Agriculture, Bureau of 

Soils. 

[11] 



MANUAL OF SOIL PHYSICS 
Questions : 

1. What are the colors of the particles that compose the sand? 

2. What is the difference in the color of the particles that 

compose the sand, the surface soil, the subsoil, and the 
clay ? Why are soil particles so similar in their mineral 
content ? 

3. What is the range, in millimeters, in the size of sand parti- 

cles ? silt particles ? clay particles ? 

4. AVhat is the structure of the surface-soil particles ? How do 

you account for such a structure ? 

5. By what means can you distinguish the organic matter in 

the different soils while under the microscope ? 

6. Define sand, silt, clay, and loam. 



[12] 



EXERCISE VI 



SOIL-FORMING MINERALS 



Object. The object of the exercise is to become familiar 
with the most important soil-forming minerals. 

Materials needed. Specimens of qnartz, feldspar, mica, talc, 
hornblende, calcite, gypsum, dolomite, iron ores, serpentine ; 
gravel ; microscope ; mortar and pestle ; hydrochloric acid. 




Fig. 2. Common soil-forming minerals 



Procedure. Study the above-named minerals, describing 
each according to the following outline : 

1. Name. 

2. Crystalline or amorphous. 

3. Cleavage (number of planes). 

4. Fracture (conchoidal or irregular). 

5. Colors. 

6. Luster. 

7. Hardness. 

8. Effect of hydrochloric acid. 

[13] 



MANUAL OF SOIL PHYSICS 

9. Composition. 

10. Kind of soil formed. 

11. Per cent in earth's crust. 

12. Miscellaneous. 

After describing each mineral select about half a dozen 
pebbles of the mineral from the gravel. Place them in the 
mortar and pulverize them, examining the broken pieces from 
time to time, noting the constancy of the cleavage and fracture 
characteristics. After they are pulverized examine some of the 
particles with the microscope, noting the same characteristics. 

References : 

Lyon and Fippin : Soils, pp. 4-9. 

Snyder: Soils and Fertilizers, pp. 64-67. 

Crosby: Common Minerals and Rocks, pp. 35-122. 

Questions : 

1. Write out the scale of hardness you have used in determin- 

ing the hardness of the different minerals. 

2. What is a plane of cleavage ? 

3. Does the number of cleavage planes influence the weather- 

ing qualities of a mineral ? 

4. Which minerals are found most abundantly in sand? in 

clay ? 

5. Define a mineral. 

6. Why is mica the most difficult to pulverize? 

7. Do the number of cleavage planes and the fractures remain 

true in the pulverized material ? 



[14] 



EXERCISE VII 
SOIL FORMING ROCKS 

Object. The object of the exercise is '<» become familiar 
with ili<' most important soil-forming rocl 

Materials needed. Sj>eeimeiiH of granite, linn lone, quartz- 
ite, shale, gravel, phosphate rock, sandstone; microscope; 
mortar and pestle ; hydrochloric acid. 

Procedure. Si mly the above-named rocks, describing each 
according to the following outline: 

1. Nihiic. 

2. Kind (igneous, sedimentary, or metamorphio). 
;{. Crystalline or amorphous. 

•I. ( lleavage ( number of planes). 

5. Fracture (conchoidal or irregular). 

(i. ( lolors. 

7. Luster. 

8. Hardness. 

'.». Effect of hydrochloric acid. 

I o. Composition. 

II. K ind of soil formed. 

L2. Miscellaneous. 

Alter describing each rock pulverize a small ai int in the 

mortar, noting the manner in which it bn down. Aiter 
it is pulverized examine it under the mien ope, noting the 
oleavage planes and other characteristics due to the mineral 
composition. 



MANUAL OF SOIL PHYSICS 
References : 

Lyon and Fippin : Soils, pp. 9-15. 

Crosby: Common Minerals and Rocks, pp. 35-122. 

Merrill : Rocks, Rock Weathering, and Soils, pp. 150-195. 

Questions : 

1. What is a rock ? 

2. What minerals are the most abundant in granite ? 

3. When a rock or a mineral effervesces with hydrochloric 

acid, what does this denote as to its composition ? 

4. Define igneous, sedimentary, and metamorphic rocks. 

5. Name one igneous, one sedimentary, and one metamorphic 

rock found in the state or county. 



[16] 



EXERCISE VIII 



VOLUME DENSITY AND POROSITY 

Object. The object of the exercise is to determine the vol- 
ume weight, apparent specific gravity, and pore space of soils. 

Materials needed. 
Three tubes; soils; 
balance ; graduate. 

Procedure. After 
weighing the tubes, 
fill one with sand, 
another with sur- 
face soil, and the 
third with subsoil, 
to within 1 inch 
of the top of the 
tube. Use compact- 
ing machine No. 1 
in filling the tubes, 
allowing the weight 
to fall eight times 
from the 12-inch 
mark for each small 
measure of soil 
added to the tube. 
Determine the vol- 
ume space occupied 
by each soil by 

measurements or by filling the tube to the same height with 
water and measuring the number of cubic centimeters. If the 

[17] 




II 



No. 1 



No. 



Fig. 3. 



The two designs of compacting machines 
used in these exercises 



MANUAL OF SOIL PHYSICS 

hygroscopic moisture content is not known, it must be deter- 
mined with a separate sample (see Exercise XII). 

Calculation. To obtain the apparent specific gravity of the 
soil, divide the weight of the water-free soil by the weight of 
the same volume of distilled water. 

Per cent pore spaee = 100 - Apparent specific gravity x m 

Absolute specific gravity 

Tabulate the results in a form similar to the following : 





Soil 


Weight of 
Empty Tube 


Weight of 
Filled Tube 


Weight 
of Soil 


Weight of 

Hygroscopic 

Water 


Weight of 
Water-free 
Soil in Tube 


Sand 

Surface soil 
Subsoil 


Grams 


Grams 


Grams 


Grams 


Grams 





Volume of 
Cylinder 



Weight of 
lcc. Water- 
free Soil 



Apparent 
Specific 
Gravity 



Absolute 
Specific 
Gravity 1 



Per Cent 

Soil 

Space 



Per Cent 
Pore 
Space 



Sand 

Surface soil 
Subsoil 



cc. 



Grams 



From results obtained in this exercise, compute in pounds 
the weight per cubic foot and weight per acre foot of each soil. 



Soil 



Weight per Cubic Foot in Pounds Pounds per Acre Foot 



Sand 

Surface soil 
Subsoil 



1 The average absolute specific gravity of most soils is 2.65. 

[18] 



VOLUME DENSITY AND POROSITY 
References : 

King: Physics of Agriculture, pp. 108-117. 

Lyon and Fippin : Soils, pp. 88-97. 

Wiley : Principles and Practices of Agricultural Analysis, Vol. I, 

pp. 95-99. 
Hall : The Soil, pp. 60-67. 

Questions : 

1. Explain the difference between absolute specific gravity and 

apparent specific gravity. 

2. Given a soil having an apparent specific gravity of 1.1 and a 

pore space of 58.5 per cent, what is the absolute specific 
gravity ? 

3. Given three soils, having pore spaces of 65, 55, and 45 per 

cent respectively and an absolute specific gravity of 
2.65 each, what is the apparent specific gravity of each 
soil? 

4. The apparent specific gravity of soils in the field may be 

taken as an approximate indication of the tilth of the 
soil, Explain. 

5. What factors influence the apparent specific gravity of 

soils ? 



[19] 



a 



EXERCISE IX 

NUMBER AND SURFACE AREA OF SOIL PARTICLES 

Object. The object of the exercise is to ascertain the num- 
ber and surface area of the particles in a given volume of 
different soil separates. 

Procedure. Considering the particles in each separate to be 
perfect spheres and arranged in a simple columnar structure, 
find the average number and surface area of the particles in 
a cubic foot of each of the soil separates, from coarse sand to 
clay inclusive. In obtaining the average diameter of a sepa- 
rate, use the average of the largest and smallest diameters. 
Indicate the method used in making the computation and 
tabulate your results in a form similar to the following: 



Soil Separate 


Number of Particles per 


Surface Area per Cubic 


Cubic Foot, in Millions 


Foot, in Acres 


Coarse sand 






Medium sand 






Fine sand 






Very fine sand 






Silt 






Clay 







References : 



Lyon and Fippin : Soils, pp. 80-84. 

King: Physics of Agriculture, pp. 109, 117-122. 

King : Soil Management, pp. 161-187. 

Widtsoe : Principles of Irrigation Practice, pp. 8-13. 

[21] 



MANUAL OF SOIL PHYSICS 
Questions : 

1. What are the difficulties in determining the surface area of 

soil particles accurately ? 

2. Would the number of soil particles per cubic foot be in 

creased or decreased if the soil had a single, or com- 
posite, structure? Explain. 

3. What relation exists between the number of soil particles 

and the total surface area of all soil particles in equal 
volumes of different soil classes ? 

4. Is there any relation between the total surface area of all 

soil x>articles per volume of soil and the water-retaining 
capacity? Explain. 

5. Is there any relation between the total surface area of all 

soil particles per volume of soil and the rate of chemical 
solution by which the plant-food constituents contained 
in the mineral particles become available for plant use ? 
Explain. 

6. What influence does the total surface area of all soil par- 

ticles per volume of soil have upon the quantity of food 
materials retained therein in a semiavailable form ? 
Explain. 



[22] 



EXERCISE X 



FLOW OF AIR THROUGH SOILS 

Object. The object of the exercise is to study the flow of 
air through different classes of soil. 

Materials needed. Three percolation tubes ; aspirator; large 
bottle ; graduate ; sand ; surface soil ; subsoil. 

Procedure. Fill the three percolation tubes, one with each 
class of soil, using the compacting machine in filling the tube, 
allowing the weight to fall 
three times from the 12-inch 
mark for each small meas- 
ure of soil that is added to 
the tube. 

After filling the bottle of 
the aspirator with water, 
attach the tube that ends 
near the top of the bottle 
to the tube containing the 
sand. By means of the other 
tube, siphon the water from 
the aspirator into the large 
bottle, which should be 
placed on the floor. Record 
the number of cubic centi- 
meters of air that will flow through the sand in a given time. 
The amount of water, in cubic centimeters, that flows from 
the bottle is equal to the amount of air that is drawn through 
the soil. 

[23] 




Fig. 4. Bottle aspirators, and apparatus 
for studying flow of air through soils 



MANUAL OF SOIL PHYSICS 

In a similar manner, determine how many cubic centimeters 
of air will flow through the surface soil and through the 
subsoil in the same length of time. 

Record your results in a form similar to the following : 



Sul L 



Sand 

Surface soil 
Subsoil 



Cubic Centimeters of Air in 10 Minutes 



References : 

Lyon and Fippin : Soils, pp. 432-447. 

King : The Soil, pp. 229-232. 

King: Physics of Agriculture, pp. 125-137. 

Questions : 

1. How do you account for the air flowing through the sand 

so much faster than through the subsoil ? 

2. What kinds of soils are naturally well aerated? 

3. What kinds of soils are naturally poorly aerated? 

4. Name several methods by which aeration of soils that are 

naturally well aerated may be reduced. 

5. Name several methods of increasing aeration in compact, 

fine-textured soils. 

6. What relation does aeration have to growth of organisms 

in the soil ? 



[24] 



EXERCISE XI 



PERCOLATION OF WATER 



Part I 

Object. The object of the exercise is to note the rate of 
flow of water through different classes of soil. 

Materials needed. Three percolation tubes; three beakers; 
graduate ; rubber tubing ; sand ; surface soil ; subsoil. 

Procedure. Fill the percolation tubes to within 3 inches of 
the top, one with each class of soil. In filling the tubes, use 
compacting machine No. 1, 
allowing the weight to 
fall three times from the 
8-inch mark for each small 
measure of soil added to the 
tube. Place about an inch 
of gravel on the top of each 
soil, to prevent puddling. 
Connect the tubes by means 
of short pieces of rubber 
tubing, and, by means of a 
longer piece, connect to the 

water cock. Arrange the tubes so that the water will flow over 
the top of the soil in each tube, the surplus being conveyed 
into the drain. Before taking the readings, allow the water 
to percolate through each soil a week. 

Determine the number of cubic centimeters of water that 
will flow through each soil in one half hour. 

[25] 



1 


I 


m 

1 


m 

1 


i 


! 




I 


l^w w m m w~* 







Fig. 5. Apparatus for studying perco- 
lation of water through soils 



MANUAL OF SOIL PHYSICS 



Reduce the results of Exercise X to a ratio and compare 
with the ratio of water movement. 

Tabulate your results in a form similar to the following : M 



Kind of Soil 



Sand 

Surface soil 
Subsoil 



Cubic Centimeters 
in 30 Minutes 



Relative Ratio of 
Water Movement 



Relative Ratio of 
Air Movement 



Part II 

Materials needed. Three 8-foot percolation tubes ; plotting 
paper ; loam ; silt loam ; clay. (The tubes should be prepared 
by the laboratory assistant.) 

Procedure. Take readings, every period, of the rate of 
percolation in each tube, recording your results in a conven- 
ient form. After the water has percolated through the entire 
column, take readings on the amount of water that percolates 
through each soil in twenty-four hours. 

After all the data have been collected, plot curves showing 
the rate of water movement through each soil. 



References : 

Hilgard : Soils, pp. 221-228. 
Widtsoe: Dry Farming, pp. 111-116. 
Hall : The Soil, pp. 75-79. 
King: The Soil, pp. 170-173. 

Questions : 

1. What factors influence the flow of water through soils ? 

2. What objections to a sandy subsoil does this exercise show ? 

3. In what practical way may a clay subsoil be improved ? 

4. Will water percolate most rapidly through a dry, a moist, 

or a wet soil ? Explain your answer in full. 

[26] 



EXERCISE XII 

DETERMINATION OF HYGROSCOPIC MOISTURE 

Object. The object of the exercise is to make a determina- 
tion of the amount of hygroscopic moisture in air-dry soil. 

Materials needed. Three tin boxes; balance; drying oven; 
sand ; surface soil ; subsoil. 

Procedure. Put a 20- or 30-grain sample of each air-dry 
soil into a weighed tin box, and heat in a drying oven at 
110° C. until a constant weight is reached. (Constant weight 
is usually reached, with most air-dry soils, in two and one-half 
hours.) The loss in weight is due to the loss of hygroscopic 
water. 

Determine the per cent of hygroscopic moisture in each 
sample of soil, using water-free soil as the basis of calculation. 

Tabulate the results in a form similar to the following : 





Weight 

of Can 


WeightofCan and Soil 


Weight ok 
Hygro- 
scopic 
Water 


Weight of 

Water- 
free Soil 


Per Cent 
of Hygro- 
scopic 

Water 


Soil 


Before 
heating 


After 
heating 


Sand 

Surface soil 
Subsoil 


Grams 


Grams 


Grams 


Grams 


Grams 


(iniins 





References : 



Hall : The Soil, pp. 84-88. 

Hilgard: Soils, pp. 195-201. 

Lyon and Fippin : Soils, pp. 143-145. 

[27] 






MANUAL OF SOIL PHYSICS 



Questions : 



1. Define hygroscopic water. 

2. Name the soil and climatic factors that influence the hygro- 

scopic capacity of soils. 

3. What influence does the porous condition of the various 

soil materials have upon the amount of hygroscopic 
water in a soil? 

4. Is hygroscopic moisture of utility to planl growth? l)i- 

at length. 






[28] 



EXERCISE XIII 

CAPILLARY RISE OF WATER IN SOILS 

Object. The object of the exercise is to make a detailed 
study of the upward movement of the water in different 
classes of soil when in different conditions. 

Part I 

Capillary Rise of Water in Loose Soils 

Materials needed. Three 6-foot sections of 2-inch tubing; 
sand ; surface soil ; subsoil ; ruler ; muslin ; plotting paper. 

Procedure. Fill three tubes, one with each class of soil, 
exercising care to compact the soils as little as possible. After 
placing the tubes in the tube rack and adding water, take 
readings every half hour during the period. Also take read- 
ings every day for a week and then once a week until the 
end of the exercise. 

Part II 

Capillary Rise of Water in Compact Soils 

Materials needed. Three 6-foot sections of 2-inch tubing; 
sand ; surface soil ; subsoil ; ruler ; muslin ; plotting paper. 

Procedure. Fill three tubes, one with each soil. Compact 
the tubes by tapping the sides of the tube six times after each 
measure of soil has been added. The water should be added 
to these tubes at the same time it is added to the tubes in 
Part I. Take all readings as directed hi Part I. 

[29] 



MANUAL OF SOIL PHYSICS 

Part III 

Determination of the per cent of Capillary Water 

Materials needed. Soil containers ; balance ; drying oven. 

Procedure. When the capillary water has risen as high as 
it will by capillarity or has reached the top of the tube, obtain 
samples from each tube representative of each six inches from 
the top of the water table to the top of the moist column. 
Determine the per cent of moisture in all six tubes for every 
6-inch section. 

Part IV 

Capillary Rise of Water in Loam, Silt Loam, and Clay 

Materials needed. Three 8-foot tubes; loam; silt loam; 
clay; plotting paper. (The tubes should be prepared by the 
laboratory assistant.) 

Procedure. Take readings, every period, of the rate at which 
the water rises in the three classes of soil, recording your 
results in a convenient form. 

After all the data for Parts I, II, and IV have been collected 
and tabulated in a convenient form, plot curves showing the 
capillary movement of the water as observed in each part. 

References : 

Hilgard : Soils, pp. 201-216. 
Widtsoe : Dry-Farming, pp. 106-111. 
Hall : The Soil, pp. 97-102. 
Lyon and Fippin : Soils, pp. 169-189. 

Questions : 

1. In which soil was the water rising most rapidly at the end of 

the first hour ? the 48th hour? the 112th hour? Explain. 

2. What effect does compacting a soil have upon the capillary 

movement of the water ? 

[30] 



CAPILLARY RISE OF WATER IN SOILS 

8. What factors influence the amount of water drawn up in 
soils ? 

4. What factors influence the rise of capillary water in soils? 

5. What is the effect on capillarity if wet from the top as in 

rains? Explain in full. 

6. Is the quantity of water in the moist column uniformly 

distributed? Explain in full. 

7. Why is the daily rise of water not uniform ? 



[31] 



EXERCISE XIV 

EFFECT OF ORGANIC MATTER AND DRY CLODS UPON 
CAPILLARITY 

Object. The object of the exercise is to note the effect of 
organic matter and dry clods upon the capillary rise of water 

in soils. 

Materials needed. Stand with three glass tubes ; three beak- 
ers ; ruler ; muslin ; surface soil ; clods ; compost ; sawdust. 

Procedure. Tie a piece of muslin over the bottom of each 
tube and fill each with 12 inches of surface soil. Place a 
1-inch layer of clods in one tube, a 1-inch layer of compost in 
another, and a 1-inch layer of sawdust in the third ; then fill 
the remainder of each tube with surface soil. Place the tubes 
in the stand and fill the beakers about half full with water. 
Every thirty minutes for the remainder of the period take accu- 
rate readings of the rate at which the water rises in each tube. 

Tabulate your results in a form similar to the following: 





Horns 


Snl LS 


2 


1 


n 


o 


24 


48 


Surface soil and compost . . . 
Surface soil and sawdust . . . 


Inches 


[ncht s 


Inches 


Inches 


Inches 


fitches 



References : 

Fletcher: Soils, pp. 89-96. 

Lyon and Fippin : Soils, pp. 144-160. 

- [ 33 ] 



MANUAL OF SOIL PHYSICS 

Questions : 

1. What effect does a layer of coarse organic matter have upon 

the capillary rise of water? 

2. What may be the effect of plowing under coarse organic 

matter just prior to planting corn ? 

3. What may be the effects upon capillarity if land which is 

to be planted to corn is plowed the previous fall ? 

4. Is there any reason suggested in the exercise for plowing 

the wheat land several weeks before sowing the Beed? 
Explain. 



* 



[34] 



EXERCISE XV 

POWER OF SOILS TO RETAIN WATER AGAINST 
PERCOLATION 

Object. The object of the exercise is to study the water- 
retaining power of soils in different degrees of compactness 
and containing various amounts of organic matter. 

Materials needed. Two stands of six tubes each ; sand ; sur- 
face soil ; subsoil ; compost or sawdust ; 4-gallon jar ; scales. 

Part I 
Power of Loose Soils to retain Water against Percolation 

Procedure. Weigh three tubes and record the weights in 
the proper blanks. Fill the tubes to within two inches of the 
top, one with each class of soil, exercising care not to com- 
pact the soil more than is necessary. Weigh and label the 
filled tubes. (A very convenient method of labeling is to 
place a small piece of paper on the top of the soil in the tube.) 

Determine the per cent of hygroscopic moisture in each 
sample, and the apparent specific gravity. 

Part II 

Power of Comtact Soils to retain Water against Percolation 

Procedure. Weigh three other tubes as indicated in Part I. 
Fill one tube with each class of soil. Compact the soil with 
compactor No. 2 if possible ; otherwise use machine No. 1, 

[35] 



MANUAL OF SOIL PHYSICS 

allowing the weight to fall four times from the 12-inch mark 
for each measure of soil that is added. Weigh and label as 
directed in Part I. Also r.ake all determinations as in Part I. 



Part III 

Power of Organic Matter to retain Water against 
Percolation- 

Procedure. Repeat Parts I and II, using the remaining six 
tubes. The soil, however, should be mixed with one fourth 
its volume of compost. 

Procedure in general. After filling and weighing all the 
tubes, place them in the jar and fill it with water, so thai the 
water level is a little above the level of the soil in the tubes. 
Allow them to remain in the water until the soil is thoroughly 
saturated. After saturation remove them and weigh as soon 
as possible ; then place them in the stands and allow to drain 
for two weeks. Place two inches of cotton in the tops of the 
tubes to reduce evaporation. Weigh the tubes every period 
during the two weeks and note the rate of loss in each. 

It is difficult to determine the time when the soils are 
thoroughly saturated if the water is allowed to run into the 
tubes from the top. By submerging the tubes below the level 
of the soil and allowing the water to flow up from the bot- 
tom the time of complete saturation will be indicated when 
the water appears on top of the soil. 

Calculate the weight of water, the per cent of water, the 
pounds per cubic foot, and the inches of water retained again si 
percolation in each soil. In making these calculations the 
student will find it necessary to know the apparent specific 
gravities of the samples. It is not required that a special 
determination be made at this point, provided the student has 
already obtained the figures from a previous exercise. 

[36] 



POWER TO RETAIN WATER AGAINST PERCOLATION 



Tabulate your results in a form similar to the following : 
Power of to retain Water against Percolation 



Kind of Soil 



Weight 
of Tube 



Weight of Weight of 

Tcbe and Air-dry 

Soil Soil 



Weight of 

Water- 
free Soil 



Apparent 
Specific 
Gravity 



Sand .... 
Surface soil . 
Subsoil . . . 



Grams 



Grams 



Grams 



Grams 



Kind of Soil 


Weights of Tubes and Soils after Saturation 


] >ate 


Date 


Date 




Date 


Surface soil 


Grams 


Grams 


Grams 


Grams 


Grams 



Kind of Soil 


Maximum Weight of 

Water retained 
against Percolation 


Water retained 
against Percola- 
tion 


Water retained 
per Cubic Foot 


Surface soil . . 
Subsoil .... 


Grams 


Pi r cent 


Po mul 's 


Indies 



References : 

King: Physics of Agriculture, pp. 131-141. 
Hilgard : Soils, pp. 207-214. 

Questions : 

1. Why is it important to know the water-retaining power of 

soils? Explain. 

2. Explain why the compact surface soil and subsoil will not 

hold as much water against percolation as they do when 
loose. 

3. Why does the addition of organic matter increase the 

water-holding capacity ? 



[37] 



EXERCISE XVI 

THE EFFECTIVENESS OF MULCHES 

Object. The object of the exercise is to study the effect of 
mulches to retard evaporation of moisture from the soil. 

Materials needed. Eight evaporimeters ; scales; surface 
soil; mulching materials. It is advisable that the instructor 
start this exercise, so that the student may begin at once to 
make weighings of the evaporimeters. 

Procedure. Fill the evaporimeters to within three inches of 
the top with surface soil. Over the surface of the soil in each 
evaporimeter place a 3-inch mulch in the following order: 

1. No mulch ; soil compact. 

2. No mulch ; soil compact (check). 

3. Soil mulch, cultivated three inches deep. 

4. Soil mulch, cultivated three inches deep (check). 

5. Gravel mulch. 

6. Sand mulch. 

7. Sawdust mulch. 

8. Cut-straw mulch. 

Weigh the evaporimeters every period for two or three 
weeks, and at the end of that time determine the amount of 
water that has evaporated from each evaporimeter. 

Calculate in terms of tons per acre and in inches of rain- 
fall the amount of water that has been evaporated from each 
evaporimeter. 

[39] 



MANUAL OF Soil, PHYSICS 
Tabulate your results in a form similar to the following: 



Tube No. 


Date 


Date 


Date 


Date 


1) \TE 


Date 


DAT] 


Toi \ i. 

K\ U'.'l; ITIOK 


1 


Grama 


Grams 


Grams 


Grams 


Grams 


Grams 


Grams 


llrt tins 


2 


















3 


















4 


















5 


















6 


















7 


















8 



















Ti BE NO. 


Average Amount 
hi Water evapo- 
rated in One Day 


WATEH 1 \ AI'ii- 
RATED IN One 
Day per ACRE 


Water i-.\ \ po- 

RATED IN One 


Time ri 

to EVAPOB \ti 

1 >M IM'II 


1 


Grams 


Tons 


1 IK III s 


l)inis 


2 










3 










4 










5 










6 










7 










8 











References : 

King: Physics of Agriculture, pp. 185-195. 
Lyon and Fippin : Soils, pp. 199-210. 

"Soil Mulch" in Twenty-fifth Annual Report of Nebraska Agri- 
cultural Experiment Station, pp. 124-128. 
Widtsoe : Dry-Farming, pp. 152-156. 

Questions : 

1. What climatic factors influence the evaporation of moisture 

from the soil? 

2. What constitutes a mulch ? 

[40] 



THE EFFECTIVENESS OF MULCHES 

Under what conditions may a hard, dry layer of soil be as 

effective as a loose, dry layer of soil in retarding the 

evaporation of moisture? Explain. 
Why is sand, gravel, or straw more, effective as a mulch 

than the loose soil? 
When is it practical to use the following materials as 

mulches : travel ? sand ? straw ? 



[41] 



EXERCISE XVII 
EFFECT OF WATER UPON SOIL VOLUME 

Object. The object of the exercise is to determine the per 
cent of expansion and the per cent volume shrinkage of soils. 

Materials needed. Four cans ; ruler ; sand ; surface soil ; 
subsoil ; clay. 

Procedure. Place exactly three centimeters of soil in each 
can, using one can for each class of soil. Slowly add water to 
each can until the soil is thoroughly saturated ; then measure 
the number of centimeters of expansion. Place the cans in a 
warm place and allow them to dry. When dry, take measure- 
ments of the volume occupied by each soil. 

Calculate the number of cubic centimeters of expansion and 
shrinkage, and the per cent of expansion and volume shrink- 
age based upon the original volume of the soil. 

Tabulate the results in a form similar to the following : 



Soil 


Cubic Centimeters 


Expansion on Basis 
of Original Volume 


Shrinkage on Basis 


Expansion 


Shrinkage 


of Original Volume 


Sand 

Surface soil 
Subsoil 
Clay 


cc. 


cc. 


Per cent 


Per cent 



References : 



Warrington : Physical Properties of the Soil, pp. 35-42. 

Hall : The Soil, pp. 34-35. 

Lyon and Fippin : Soils, pp. 97-99. 

[43] 



MANUAL OF SOIL PHYSICS 
Questions : 

1. What is the per cent of linear shrinkage of clay? the per 

cent of volume shrinkage ? 

2. Name the factors that influence the degree of shrinkage 

in soils. 

3. Explain the effect of shrinkage on crop growth. 

4. Give three good methods of retarding the checking of 

clay soils. 



[44] 



EXERCISE XVIII 




LOSS ON IGNITION 

Object. The object of the exercise is to determine the 
amount of organic matter in the soil when the total volatile 
matter is considered as or- 
ganic matter. 

Materials needed. Three 
crucibles ; three burners ; 
three tripods ; soils ; desic- 
cators ; balance. 

Procedure. Put about 1 
grams of each soil in sepa- 
rately weighed crucibles 
and ignite at a slow red 
heat. Stir the soil from 
time to time, noting the 
change in color. The stirring of a hot soil should never be 
attempted with a glass rod, as it is apt to chip off and cause 
trouble. After complete ignition place the crucible contain- 
ing the soil in a desiccator to cool, and then weigh. 

Note 1. A very convenient method of working the exercise is to use the 
water-free soil. If air-dry soil is used, the hygroscopic moisture content 
must be determined with a separate sample. 

Note 2. It will be frequently noticed during the process of ignition that 
the soil surface becomes darker in color. In some instances this is partially 
due to the water movement from the soil, but usually it is caused by the 
breaking up of carbon compounds and the temporary deposit of carbon on 
the surface of the soil. This temporary deposit is soon oxidized and lost as 
a gas. 

[45] 



Fig. 6. Apparatus for determining the 
loss on ignition 



MANUAL OF SOIL PHYSICS 
Tabulate your results in a form similar to the following ; 





Weight 

of 
Cruci- 
bles 


Weight of 
Crucible 
and Soil 


Loss 

BY 

Igni- 
tion 


Weight 

OF 

Water- 
free 
Soil 


Loss 
in Or- 
ganic 

Mat- 
ter 


Organic Matter 
Calculated in 


Soil 


Before 
igni- 
tion 


After 
igni- 
tion 


Per 

cent 


Pounds 
per 
cubic 

foot 


Tons 
per 
acre 
foot 


Sand 

Surface soil 
Subsoil 


Grams 


Grams 


Grams 


Grams 


Grams 


Grams 









References : 

Lyon and Fippin : Soils, pp. 124-127. 
Hall : The Soil, pp. 42-47. 

"Changes in the Composition of the Loess Soil," in Bulletin 
No. Ill of the Nebraska Agricultural Experiment Station. 

Questions : 

1. Why do soils change color upon ignition? 

2. What is organic matter ? 

3. Distinguish between organic matter and humus. 

4. What essential plant-food elements are removed from the 

soil by ignition? 



[46] 



EXERCISE XIX 



SOIL ACIDITY AND BASICITY 

Object. The object of the exercise is to study the method 
of determining whether a soil is acid or basic. 

Materials needed. Blue and red litmus paper; two evapo- 
rating dishes ; distilled water ; soils. 

Procedure. In testing a soil with litmus paper the greatest 
care must be exercised. All apparatus must be clean, and the 
paper must not be handled 
with sweaty fingers. 

Fill one of the evaporat- 
ing dishes nearly full with 
soil and moisten with dis- 
tilled water. Place a piece 
of the red litmus paper on 
the soil ; press it down with 
a clean knife blade, so that 
it is well in contact with 
the soil. In a similar man- 
ner place a piece of blue 
litmus paper on the same 
soil on the opposite side of 
the dish from the red paper ; allow it to stand for ten min- 
utes, and then observe results. Care must be taken not to 
confuse the two pieces of paper. 

After making one determination procure unknown samples 
from the instructor, and determine whether they are acid or 
basic. Report your results to the instructor. 

[47] 




Fig. 7. 



Testing soils with litmus paper 
for acidity 



MANUAL OF SOIL PHYSICS 
References : 

"Acid Soils," in Bulletin No. 90 of the Oregon Agricultural 

Experiment Station. 
Fletcher : Soils, p. 401. 

Van Slyke : Fertilizers and Crops, pp. 140-144. 
"Soil Acidity and Liming," in Bulletin No. 230 of the Wisconsin 

Agricultural Experiment Station. 



[48] 



EXERCISE XX 

DETERMINATION OF HUMUS 

Object. The object of the exercise is to determine the 
amount of humus in soils. 

Materials needed. Two 250-cc. Erlenmeyer flasks ; balance ; 
distilled water ; hydrochloric acid (4 per cent solution) ; am- 
monium hydroxide (5 per cent solution) ; two glass funnels ; 
filter paper ; two beakers ; graduate ; burner ; tripod ; two 
evaporating dishes ; water bath ; water-free surface soil. 

Procedure. 

1. Weigh two samples of from 10 to 15 grams of water- 
free surface soil and place in separate flasks. 

2. Add to each flask 100 cc. of 4 per cent hydrochloric 
acid and allow to digest for at least twenty-four hours. 

3. Transfer the soil to a filter in a funnel, and filter off all 
the acid, discarding the filtrate. Wash the soil thoroughly 
with distilled water. 

4. After the soil has been thoroughly washed, pass 5 per 
cent ammonium hydroxide through the soil until the filtrate 
is entirely clear or does not give a precipitate when treated 
with hydrochloric acid. 

5. Transfer the filtrate to an evaporating dish and evapo- 
rate to dryness ; then dry for one hour at 100° C. 

6. When dry, weigh and ignite at a red heat ; thenreweigh. 
The loss in weight is humus. 

7. Calculate the per cent of humus in the sample and in 
terms of pounds per acre foot. 

[49] 



MANUAL OF SOIL PHYSICS 
Record your results in a form similar to the following 





Weight of Evaporating 
Dish and Residue 


Weight 

of 
Humus 


Per Cent 

of 

Humus 


Pounds 
per 




Before 
ignition 


After 
ignition 


Acre 

Foot 


First sample 
Second sample 


Grams 


Grams 


Grams 







References : 

Hilgard : Soils, p. 132. 

Wiley : Principles and Practices of Agricultural Analysis, pp. 357- 

366. 
Widtsoe : Dry-Farming, pp. 58-59. 
Snyder: Soils and Fertilizers, pp. 103-116. 

Questions : 

1. What is the material left in the evaporating dish after the 

humus has been driven off by ignition ? 

2. What are some of the defects of the Grandeau method of 

humus determination? 

3. Describe the formation of humus in the soil. 

4. Discuss the relative plant-food values of humus found in 

humid and in arid regions. 



[50] 



EXERCISE XXI 



LEACHING OF SOILS 

Object. The object of the exercise is to study the leaching 
of soils. 

Materials needed. Three glass tubes in stand ; muslin ; three 
beakers ; distilled water ; graduate ; sand ; surface soil ; subsoil. 

Procedure. Tie a piece of muslin over the small end of the 
tubes and place 6 inches of sand in one tube, 6 inches of 
surface soil in a second, and 
6 inches of subsoil in the 
third. Place the filled tubes 
in the stand and pour 50 cc. 
of distilled water into each. 
Allow the water to perco- 
late into the beakers, which 
are placed under the tubes. 

Observe the color of the 
water after it has perco- 
lated through each soil. 
The first two or three drops 
should be compared with the last few drops as to their color. 
Write a brief summary of your observations and conclusions. 

References : 

Hilgard : Soils, pp. 22-28. 

Widtsoe : Dry-Farming, pp. 65-66. 

Hopkins: Soil Fertility and Permanent Agriculture, pp. 556-561. 

King : Physics of Agriculture, pp. 77-79. 

[51] 




Fig. 8. Apparatus for studying leaching 
of soils 






MANUAL OF SOIL PHYSICS 



Questions : 

1. Why does the water become colored in passing through 

the soil? 4— 

2. What undesirable effects of heavy rains are suggested in 

this exercise? Explain. 

3. Can leaching be retarded ? Explain the methods. 

4. What salts are least liable to be leached from the soil ? 

5. The humid soils contain 15 per cent less soluble material 

than arid soils and, as compared with the semiarid re- 
gion, 9 per cent less soluble material. 1 Is this condition 
due to the power of the soil to retard leaching or to cli- 
matic factors . ; Explain. 

1 Lyon and Fippin : Soils, p. 66. 



; 



[52] 



EXERCISE XXII 

POWER OF SOILS TO ABSORB SALTS 

Object. The object of the exercise is to study the absorp- 
tive power of different classes of soil. 

Materials needed. Three glass tubes in stand ; three beakers ; 
muslin ; graduate ; eosin solution ; sand ; surface soil ; subsoil. 

Procedure. Tie a piece of muslin over the small end of each 
tube and place 6 inches of sand in one tube, 6 inches of 
surface soil in another, and 6 inches of subsoil in a third. 
Place the filled tubes in the stand and pour two inches of the 
solution over each soil. Place beakers under the tubes to 
catch the solution that percolates through the soil. 

Note carefully the color of the first two or three drops that 
percolate through each soil, and compare it with the last 
drops that percolate through. Write a brief summary of 
your observations and conclusions. 

References : 

Snyder : Soils and Fertilizers, pp. 191-197. 

Hopkins : Soil Fertility and Permanent Agriculture, pp. 562-564. 

Hall : The Soil, pp. 211-232. 

Fraps : Principles of Agricultural Chemistry, pp. 234-243. 

Questions : 

1. Do all soils have some power to absorb salts ? 

2. Make a comparison of the color of the solutions that drip 

from each class of soil. 

3. What salts do not undergo fixation ? 

4. Why is it important that soils have the power of absorption ? 

5. What factors influence the power of absorption? 

[53] 



■\ 



EXERCISE XXIII 
ABSORPTION OF GASES BY SOILS 

Object. The object of the exercise is to study the power of 
soils to absorb gases. 

Materials needed. Four air-tight containers ; four watch 
glasses ; sand ; surface soil ; subsoil ; ammonia water. 

Procedure. In one of the containers place about 50 grams 
of sand ; in the second, 50 grams of surface soil ; and in the 
third, 50 grams of subsoil. No soil is placed in the fourth 
container. Pour a few drops of ammonia water on each of the 
watch glasses and place one in each container. Cover the 
container so that none of the ammonia gas can escape. Put 
the containers away until the next period. At the next labor- 
atory period open and try to detect the odor of ammonia in 
each container. 

References : 

Hall : The Soil, pp. 214-216. 
Hilgard : Soils, pp. 272-276. 

"Absorption of Vapor and Gases by Soils," in Bulletin No. 51 of 
the United States Department of Agriculture, Bureau of Soils. 

Questions : 

1. What differences can you notice in the odor of the four 

containers after letting them stand from one period to 
the next? Name the soils in the order of their greatest 
apparent absorptive power. 

2. Is absorption a physical or a chemical process? 

3. What is absorption ? 

4. How is this exercise related to the application of organic 

matter ? 

[55] 



EXERCISE XXIV 

ABSORPTION OF MOISTURE BY SOILS 

Object. The object of the exercise is to study the power 
of soils to absorb moisture when placed in a saturated 
atmosphere. 

Materials needed. Six tin boxes ; plotting paper ; thermom- 
eter; water-free soils; compost; balance; moist-air chamber. 

Procedure. "Weigh 20 grams of water-free sand, surface 
soil, subsoil, clay, and compost in separately weighed boxes. 
Place them, with the covers removed, in the moist-air chamber. 
Place the empty can in the moist-air chamber, to determine 
the amount of moisture that collects on it. Ascertain the 
weight of each can at the end of 24, 48, 72, and 96 hours, 
recording each time the temperature of the air in the chamber. 

Note. In making the weighings do not leave the lid of the moist-air 
chamber open any longer than necessary, as it causes a change in the 
humidity of the atmosphere. Make all weighings as rapidly as possible, 
in order that the loss by evaporation may be reduced to a minimum. 



Tabulate your results in a form similar to the following 



Soil 


Tempera- 
ture 


Water absorbed during 


1st 24 hrs. 


2d 24 hrs. 


3d 24 hrs. 


4th 24 hrs. 


Total 


Sand . . . 
Surface soil . 
Subsoil . . 
Clay. . . . 
Compost . . 


Degrees 


Per cent 


Per cent 


Per cent 


Pi r -lit 


Per cent 



[57] 



MANUAL OF SOIL PHYSICS 

Plot curves showing the amount of absorption by each soil 
as indicated by the data. 

References : 

Hilgard : Soils, pp. 196-200. 

Hall : The Soil, pp. 84-89. 

"The Wilting Coefficient for Different Plants and its Indirect 
Determination," in Bulletin No. 230 of the United States De- 
partment of Agriculture, Bureau of Plant Industry. 

Questions : 

1. What is meant by the maximum hygroscopic coefficient 

of soil? 

2. What relation exists between the maximum hygroscopic 

coefficient and the wilting coefficient of soils? 

3. What practical applications may be made of the determina- 

tions for the maximum hygroscopic coefficient of soils ? 

4. What factors influence the absorption of moisture from 

the air? 

5. Why should the temperature be kept as nearly constant 

as possible? 



[58] 



EXERCISE XXV 

FLOCCULATION OF CLAY 

Object. The object of the exercise is to study the flocculat- 
ing effect of various materials on clay particles in suspension. 




Fig. 9. Apparatus for studying flocculation 

Materials needed. Four glass cylinders ; clay ; distilled 
water; 1 per cent ammonia solution; alum; limewater; 
pipette ; microscope. 

Procedure. Place 20 grams of clay in one of the cylin- 
ders and fill with distilled water. Stir thoroughly the con- 
tents of the cylinder, and after five minutes of sedimentation 
decant the turbid liquid into a second cylinder, rejecting all 
the sediment. Divide the turbid liquid into four equal por- 
tions. To one of the cylinders add 20 cc. of limewater ; to the 
second, 10 cc. of ammonia water ; and to the third, 0.1 grams 

[59] 



MANUAL OF SOIL PHYSICS 

of alum. Fill all four cylinders with distilled water, stir, and 
set aside, observing the results. After twenty-four to forty- 
eight hours examine, with the aid of a microscope, some of 
the particles in each cylinder. Procure a sample for the 
mount from the bottom of the cylinder by the use of the 
pipette. Care should be taken not to destroy the structure 
of the floccules. 

Take careful notes on the rate of flocculation in the four 
cylinders, as well as the time required for the water to be- 
come comparatively clear. Write a brief summary of your 
observations. 

References : 

Hall : The Soil, pp. 38-41. 

Van Slyke : Fertilizers and Crops, pp. 103-104. 

" The Effect of Soluble Salts on the Physical Properties of Soil," 
in Bulletin No. 82 of the United States Department of Agricul- 
ture, Bureau of Soils. 

Questions : 

1. In which cylinder does the turbid water first become clear? 

2. What is the physical effect of liming clay soils? Explain. 

3. Define flocculation. 

4. What materials will cause flocculation? 

5. What materials will cause deflocculation ? 



[60] 



EXERCISE XXVI 

EFFECT OF LIME ON SOIL STRUCTURE 

Object. The object of the exercise is to study the crumbling 
or granulating effect of lime on clay soils. 

Materials needed. Three pans ; air-slaked lime ; clay. 

Procedure. Place about half an inch of clay in each of the 
three pans. Add to one of the pans one eighth as much air- 
slaked lime as there is soil in the pan ; to a second pan add 
one fourth as much lime as there is soil ; leave the third pure 
clay. Mix the lime thoroughly with the soil in the two pans, 
taking care that no lumps remain. Add to each pan enough 
water to saturate it ; then place all three pans where they 
will dry. Do not stir the soil after adding the water. 

As soon as the soils are dry, make drawings of each soil, 
showing the cracks that have been formed. Afterwards ex- 
amine each soil carefully, noting the physical condition and 
comparative hardness. 

References : 

Lyon and Fippin : Soils, pp. 116-118. 

Hall : Fertilizers and Manures, pp. 253-257. 

Hopkins : Soil Fertility and Permanent Agriculture, pp. 160-182. 

Questions : 

1. What is the effect of lime on the cohesiveness of the soil 

particles ? 

2. In what form and in what amounts should lime be applied 

to a clay soil to change the structure ? 

3. In which pan is the soil the hardest? the softest? Why? 

[61] 



EXERCISE XXVII 

EFFECT OF SAND AND ORGANIC MATTER ON SOIL 
STRUCTURE 

Object. The object of the exercise is to study the effect of 
sand and organic matter upon the texture and structure of soils. 

Materials needed. Three pans ; sand ; sawdust ; clay. 

Procedure. Place one half inch of clay in one of the pans 
and add to it one eighth as much sand, mixing it thoroughly. 
In a similar manner, place as much clay in another pan and 
add one eighth as much sawdust, mixing it well with the soil. 
Fill the third pan with an equal amount of clay, then add 
sufficient water to make the contents of each pan in a slushy 
condition, and put them away to dry. 

When dry, make drawings of the soils, showing the cracks. 
Work over the material in each pan, noting carefully the 
structure and hardness of each soil. 

References : 

Lyon and Fippin : Soils, pp. 113-116. 

Van Slyke : Fertilizers and Crops, pp. 134-140. 

Questions : 

1. In which pan is the soil the hardest? the softest? Why? 

2. From the results of the exercise, is it advisable to add 

organic matter to the fine-textured soils to alter their 
physical condition? 

3. When is it practical to add sand to a soil in order to 

change the texture and the structure? 

4. What are the most important physical properties of soils that 

are modified by the addition of sand or organic matter? 

[63] 



EXERCISE XXVIII 

EFFECT OF ALTERNATE WETTING AND DRYING ON 
SOIL STRUCTURE 

Object. The object of the exercise is to study the effect of 
alternate wetting and drying on the structure of soils. 

Materials needed. Six pans ; spatula ; surface soil ; clay. 

Procedure. Place 150 grams of surface soil in each of three 
pans and mix to a pasty mass. Use the spatula in mixing the 
soil, destroying any crumb structure that may exist. Put 
the pans in a warm place and allow the soils to dry. When 
dry, add a sufficient amount of water to two of the pans to 
saturate the soil, but do not stir it. Allow them to dry, and 
again wet one of the pans and again allow it to dry. In each 
of the other three pans mix 150 grams of subsoil to a pasty 
mass and treat in the same manner as the surface soil. 

After the soils are thoroughly dried, make a comparative 
study of the soils in each pan, noting the compactness and 
friability. Crumble a little of the soil from each pan between 
the thumb and finger, noting its relative hardness. Write a 
brief discussion of your observations, accounting for the dif- 
ferences in the soils. 

References : 

Lyon and Fippin : Soils, pp. 105-108. 

"Moisture Content and Physical Condition of Soils," in Bulletin 

No. 50 of the United States Department of Agriculture, Bureau 

of Soils. 

[65] 



MANUAL OF SOIL PHYSICS 
Questions : 

1. Why does alternate wetting and drying change the struc- 

ture of soils? 

2. From the results of this exercise, may there be any benefit — 

derived from plowing clayey soils before the fall rains ? 

3. Why are soils that have been wetted more than once, more 

granular in structure than soils that have been wetted 
only once? 

4. Would a sandy soil (75 per cent sand) show the same effect 

of wetting and drying? 



[66] 



EXERCISE XXIX 

EFFECT OF ALTERNATE FREEZING AND THAWING ON 
SOIL STRUCTURE 

Object. The object of the exercise is to study the effect of 
alternate freezing and thawing on soil structure- 
Materials needed. Four pans ; surface soil ; clay. 

Procedure. Mix to a pasty mass 150 grams of surface soil 
in each of two pans and 150 grams of clay in each of the other 
two pans. Place one of the surface-soil pans and one of the 
subsoil pans where they will freeze, and the other pan of each 
soil where they will dry out slowly. After the soils in the two 
pans are frozen, put them in a warm place until they thaw 
out, and again allow them to freeze. Repeat this process of 
freezing and thawing twice ; then dry the soils out slowly. 

When the soils are dry, determine the relative hardness of 
each, noting any differences that may exist hi the structure 
of the soils. 

References : 

Lyon and Fippin: Soils, pp. 108-111. 
Hilgard : Soils, pp. 118-119. 

"Physical Improvement of Soils," in Circular No. 82 of the 
Illinois Experiment Station. 

Questions : 

1. From the results of the exercise, would it be advisable to 
hold water in the surface soil in the fall of the year, so 
that the soil would be subject to a greater freezing and 
thawing ? 

[67] 



MANUAL OF SOIL PHYSICS 

2. Which is the most effective in producing a desirable struc- 

ture, alternate freezing and thawing or alternate wetting 
and drying ? 

3. Why does the alternate freezing and thawing change the fPB 

structure of the soil ? 
1. Why are the clay soils of some Southern states in pc>" 

tilth in the spring than similar soils in the Northern 

states ? 
5. Give illustrations showing the same effects of freezing and 

thawing on materials other than soil. 



[68] 



EXERCISE XXX 



EFFECT OF COLOR ON SOIL TEMPERATURE 

Object. The object of the exercise is to study the effect of 
color on soil temperature. 

Materials needed. Two thermometers ; black and white 
cloths ; five flower pots, three white and two black ; sand ; 
surface soil; subsoil. 

Procedure. Fill one of the black pots with surface soil, 
and fill one of the white pots with sand and one with subsoil. 
After taking temperature 
readings in all of the pots 
at depths of 1, 2, and 3 
inches, place them in the 
full sunlight. 

Fill the other black pot 
with surface soil, covering 
the top with 1 inch of char- 
coal. Fill the remaining 
white pot with surface soil 
and cover with i inch of 




Fig. 10. Method of studying soil 
temperature 



lime. After taking readings at depths of 1, 2, and 3 inches, 
place them in the full sunlight. 

Hang the two colored cloths in the full sunlight and at the 
end of fifteen minutes take temperature readings 1 inch from 
the back of the cloths. If the thermometer is held against 
the cloth or too far back from it, the reading taken will be 
useless for this exercise. 

[69] 



MANUAL OF SOIL PHYSICS 

Take readings every half hour during the period, recording 
the results in a form similar to the following : 





Sand 


Surface Soil 


Subsoil 


Depth 


Original 


Hours 


Original 


Hours 


Original 


Hours 




i 


1 


li 


i 


1 


11 


i 


1 


li 


L inch . . . 

2 inches . . 

3 inches . . 





























Light Covering 


Dark Covebing 


Depth 


Original 


Hours 


i tariginal 


Hours 




i 


1 


1J 


1 


1 


U 


1 inch 


















2 inches 




3 inches 









White cloth Black cloth 



References : 

Hall : The Soil, pp. 126-128. 

King: Physics of Agriculture, p. 217. 

Questions : 

1. How does color affect the temperature of the soil? 

2. How does the color of a soil affect its heat-retaining power ? 

3. Mention the soil factors to be taken into account in con- 

sidering the effect of color on the temperature of field 

soils. 

4. How much difference is there in the temperature of the 

three classes of soils at the end of the period ? 



[70] 



EXERCISE XXXI 
EFFECT OF WATER ON SOIL TEMPERATURE 

Object. The object of the exercise is to study the effect of 
water on soil temperature. 

Materials needed. Six flower pots ; two thermometers ; 
sand ; surface soil ; subsoil. 

Procedure. Prepare wet and dry samples of each class of 
soil in the flower pots. Take accurate temperature readings 
at the immediate surface, 1 inch deep, and 2 inches deep ; 
then place them in the full sunlight. Take temperature 
readings every half hour during the period. 

Record the results of each class of soil in a form similar to 
the following: : 





Time 


Temperature of Dry Sand 


Temperature of Wet Sand 


Surface 


lin. 


2 in. 


Surface 


lin. 


2 in. 


Original .... 
£ hour 

1 hour 

1£ hours .... 

2 hours .... 















References 



Snyder : Soils and Fertilizers, pp. 46-47. 

King : The Soil, pp. 225-228. 

"An Investigation of Soil Temperature and Some of the Most 
Important Factors Influencing It," in Michigan Technical Bul- 
letin No. 17, 1913. 

[71] 



MANUAL OF SOIL PHYSICS 



Questions : 

1. How does evaporation affect the temperature of the soil ? 

2. Why is a drained soil warmer than an undrained soil ? 

3. What are the chief causes which make undrained clayey 

soils cooler than well-drained sandy soils? 

4. At what time of the year is there the greatest difference 

between the temperature of the drained soil and that of 
the undrained soil? the least? Why? 

5. The temperature of the air 9 inches above the drained 

soil is higher than the temperature 9 inches above the 
undrained soil. Why? 

6. What is the specific heat of soil as compared with the 

specific heat of water? 



[72] 



EXERCISE XXXII 

EFFECT OF VEGETATION AND TOPOGRAPHY ON SOIL 
TEMPERATURE 

Object. The object of the exercise is to study the effect of 
vegetation and topography on soil temperature. 

Materials needed. Three-foot auger; two thermometers. 

Procedure. In taking soil temperatures the following points 
must be kept in mind : 

1. The temperature of the atmosphere. 

2. The direction and velocity of the wind. 

By means of the auger make a hole 18 inches in depth 
and immediately place a thermometer in the bottom and 
press the bulb into the soil. At the same time insert the 
bulb of the second thermometer into the soil to a depth of 
3 inches. Make all final temperature readings an average of 
three readings taken within a radius of 2 feet. 

In this manner study the temperature of the soils on dif- 
ferent slopes, comparing them also with the temperatures of 
level land. Make a study of the temperatures of soil covered 
Avith green vegetation, trees, and grass, comparing them with 
the temperatures of bare land. 

Tabulate your results in a form similar to the following : 





SUMMARY OF READINGS 




Depth in Inches 


Exposure of Slope 


Kind of Vegetation 






Level 


South 


North 


Trees 


Grass 




3 














18 















[73] 



MANUAL OF SOIL PHYSICS 
References : 

Hall : The Soil, pp. 120-126 ; 133-135. 
Lyon and Fippin : Soils, pp. 448-464. 

Questions : 

1. Which slope has the highest temperature ? Why ? 

2. AVhy is the ujiper 3 inches of the soil warmer than the soil 

18 inches down? 

3. Why does growing vegetation keep the temperature of the 

soil more uniform ? 

4. Explain why the exposure of the slope affects the tempera- 

ture of the soil. 



^ 



[74] 



EXERCISE XXXIII 
EFFFCT OF CULTIVATION ON SOIL TEMPERATURE 

Object. The object of the exercise is to study the effect of 
cultivation on soil temperatures. 

Materials needed. Three-foot auger ; two thermometers. 

Procedure. By means of the auger make a hole 18 inches 
deep in a field that has been recently plowed. As soon 
as possible place a thermometer in the hole, pressing the 
bulb into the soil. At the same time insert the bulb of the 
second thermometer in the soil to a depth of 3 inches, and 
after it has become constant, record the temperature. 
Make all final temperature readings an average of three read- 
ings taken within a radius of 2 feet. In this manner study 
the temperatures of soils that have received no cultivation. 
Also take careful notes on the weather conditions, slope, and 
vegetation. 

Tabulate your results in a form similar to the following : 

SUMMARY OF READINGS 



Depth in 
Inches 


Cultivated 


Uncultivated 


Cultivated 
Vegetation 


Uncultivated 
Vegetation 


3 










18 











References : 

Snyder : Soils and Fertilizers, pp. 46-51. 
Hilgard : Soils, pp. 301-310. 

[75] 



MANUAL OF SOIL PHYSICS 
Questions : 

1. What effect does the loose structure have on the tempera- 

ture of the soil ? 

2. How can a farmer aid in warming up the soil in the 

spring ? 

3. What factors influence the temperature of soils ? 

4. Why is the temperature of the upper three inches of the 

cultivated soil warmer than the upper three inches of 
the uncultivated soil? 

5. From what sources does the soil receive its heat? 



[76] 



EXERCISE XXXIV 



SOIL TENACITY 

Object. The object of the exercise is to determine the 
tensile strength of different classes of soils. 

Materials needed. Tenacity apparatus ; pan ; graduate ; 
spatula ; scales ; surface soil ; subsoil ; clay. 

Procedure. 1. Weigh 300 grams of soil and add water 
until you consider the greatest degree of stickiness reached, 
keeping a record of 
the amount of the 
water. Mix well. 

2. Place the two 
parts of the soil 
container together 
on a level surface 
and lock firmly. 

3. Fill the con- 
tainer level full 
with the moistened 
soil, leaving no air 
spaces along the 
sides. 

4. Attach the filled container directly underneath the beam 
of the apparatus. 

5. Unlock the container, exercising care not to jar or break 
the soil column. 

6. Through a small funnel add sand to the other side of the 
beam until its weight is sufficient to break the soil column. 

[77] 




Fig. 11. Method of studying soil tenacity 



MANUAL OF SOIL PHYSICS 



7. Weigh the sand. 

8. Weigh the movable part of the container with the soil 
it contains. 

9. Determine the tensile strength by subtracting the weight 
of the container, plus the soil it contains, from the weight of 
the sand. 

10. To another 300-gram sample of the same soil add 15 cc. 
more water than was added to the first sample, and to a third 
300-gram sample add 15 cc. less water than was added to the 
first sample, and in like manner determine their degree of 
tenacity. 

Record results in a form similar to the following : 





Surface Soil 


Subsoil 


(LAV 




1st 


2d 


3d 


1st 


2d 


3d 


1st 


2d 


3d 


Amount of water added . 

Weight required to break 
soil column 

Weight of soil and mov- 
able container .... 

Tenacity 





















References : 

Lyon and Fippin : Soils, pp. 97-99. 

Warington : Physical Properties of the Soil, pp. 23-25. 



Questions : 

1. What is meant by tenacity of soils? 

2. What factors determine the tenacity of soils ? 

3. About what per cent of water gives the greatest degree of 

tenacity in each soil ? 

4. Explain the relation between tenacity and the expansion 

and contraction of soils upon wetting and drying. 

5. Give your opinion as to the desirability of the property of 

tenacity in field soils. 

[78] 



EXERCISE XXXV 

TRANSFERENCE OF HEAT IN SOILS 

Object. The object of the exercise is to study the heat- 
transferring power of soils. 

Materials needed. Heat-transference apparatus ; seven ther- 
mometers ; flask ; ruler ; burner and tripod ; asbestos gauze ; 
distilled water ; sand ; surface soil ; subsoil. 




Fig. 12. Apparatus for studying transference of heat in soils 

Procedure. 1. Place 950 cc. of distilled water in the flask 
and heat to boiling. 

2. While the water is heating, fill the transference apparatus 
with sand, packing it as uniformly as possible. Place thermom- 
eters in the sand with the bulbs 2 inches below the surface 
at distances of 1, 2, 3, 4, 5, and 6 inches from the tank. As 
soon as they have become constant, record the temperature 
indicated by each. 

[79] 



MANUAL OF SOIL PHYSICS 

3. On a piece of notebook paper rule a form similar to the 
one indicated below, in which to record your readings. 

4. As soon as the water is boiling and the thermometers 
have reached a constant temperature, pour the boiling water 
into the tank, recording the exact time at which this is done. 
Immediately, by means of tubing, conduct a current of steam 
from the steam pipe into the water, in order to maintain a 
constant temperature. 

5. Use the seventh thermometer to ascertain the temper- 
ature of the water. The cork may be removed from the 
opening from time to time in taking these readings. 

6. Record the temperature indicated by each thermometer 
at the end of every 5-minute period for at least an hour 
and a half. 

7. In the same manner determine the heat-transferring 
power of the surface soil and the subsoil. 

After obtaining the results, plot curves showing the rate of 
heat-transference in each soil. (A convenient method of plot- 
ting the curves is to use one sheet for each soil.) 

Tabulate the results in a form similar to the following : 





Time 


Temperature of Water 


Distance from the Heat Source 




1 in. 


2 in. 


3 in. 


4 in. 


5 in. 


6 in. 


Min. 


Degrees 


Degrees 


Degrees 


Degrees 


Degrees 


Degrees 


Degrees 



















References : 



" Heat Transference in Soils," in Bulletin No. 59 of the United 
States Department of Agriculture, Bureau of Soils. 

Technical Bulletin No. 17 of the Michigan Agricultural Experi- 
ment Station. 



Questions : 

1. What factors influence the heat transference of soils? 

2. Summarize the conclusions as set forth in the first reference. 

[80] 



EXERCISE XXXVI 

ABSOLUTE SPECIFIC GRAVITY OF SOIL 

Object. The object of the exercise is to make determinations 
of the absolute specific gravity of soils. 

Materials needed. Pycnometer; balance; distilled water; 
thermometer ; water bath ; water-free soil. 

Procedure. 1. Fill a pycnometer bottle to the upper end of 
the capillary tube with distilled water. Wipe dry and weigh 
to three decimal places. Note the temperature of the water 
used. 

2. Empty the water and again weigh. Add about ten grams 
of water-free soil and again weigh. The difference in the two 
weights represents the exact amount of soil used. 

3. Fill the bottle about half full with water and place it in 
a shallow water bath, heating it until all the air is expelled 
from around the particles. 

4. Reduce the temperature of the water in the pycnometer 
to the original temperature, completely fill with distilled 
water, and weigh. 

Calculation. To the weight of the water-free soil, add the 
weight of the flask filled with water, and deduct the weight 
of the flask filled with the soil and water. The difference 
expresses the weight of the volume of water equal to the 
quantity of soil used. The specific gravity can therefore be 
determined by dividing the weight of the soil used by the 
weight of the water it has displaced. 

[81] 



MANUAL OF SOIL PHYSICS 
Record your results in a form similar to the following : 



Soil 


Weight of 
Flask filled 
with Water 


Weight of 

Dry Soil 

taken 


Weight of 

Flask filled 

with Water 

and Soil 


Weight of 
Water dis- 
placed nv 
Soil 


Specific 
Gb wity 


Sand 

Surface soil 
Subsoil 


Grams 


(Irams 


Grams 


Grams 


drains 



References : 

Lyon and Fippin : Soils, pp. 94-97. 

Merrill : Rocks, Rock Weathering, and Soils, pp. 40-42. 

Questions : 

1. Define absolute specific gravity. 

2. Why is it necessary to use water-free soil for the deter- 

mination of the absolute specific gravity? 

3. Why must all the air be driven out before the last weight 

is taken ? 

4. What factors influence the absolute specific gravity of 

soils ? 

5. How do you account for the small differences between the 

absolute specific gravities of the different soils ? 



[82] 



EXERCISE XXXVII 



APPARENT SPECIFIC GRAVITY OF FIELD SOILS 

Object. The object of the exercise is to determine the appar- 
ent specific gravity and pore space of soils under field conditions. 

Materials needed. Sampling auger; mallet; six sacks; bal- 
ance ; three cans ; drying oven. 

Procedure. By means of the auger secure a foot sample of 
the first foot of soil from three fields: an alfalfa field, a 
pasture, and a recently 
plowed field. In using the 
auger the tube is driven 
into the soil to such a 
depth that when the auger 
blade is just resting on 
the surface of the soil, the 
gauge may be set in the 
first notch and at the same 
time rest on the top of the 
tube. Raise the gauge one 
notch, and by turning the 
auger remove the first 
inch of soil, placing it in 
one of the sacks. In the 
same manner remove the 
soil from the first foot, 
placing it all in one sack 
if possible. It is best not 
to attempt to remove more than 1 inch of soil at a time, 
and under no consideration should more than 2 inches be 

[83] 




Fig. 13. Nebraska Soil Auger and 
sample boxes 



MANUAL OF SOIL PHYSICS 

-emoved at a time. After weighing the entire amount of soil 
amoved, take a small sample of about 100 grams and deter- 
nine the moisture content ; then calculate the weight of water- 
:ree soil. In calculating the volume of soil removed, use the 
liameter of the auger bit as the diameter of the boring. 

From the data collected determine the apparent specific 
gravity, per cent pore space, weight per cubic foot, and 
veight per acre foot for each field. 

Tabulate your results in a form similar to the following : 



Kind of Field 


Apparent 
Specific Gravity 


Porosity 


\\ i u, in ii B 

< i arc Foot 


Ul h.HT PEE 

\. be Poor 


\lfalfa .... 
*asture .... 
lecently plowed 




Per cent 


/'mi in Is 


Tons 





References : 

Exercise No. 8 (for method of calculation). 
King: Physics of Agriculture, pp. 110-117. 
Hall : The Soil, pp. 60-67. 
Lyon and Fippin : Soils, pp. 88-97. 

Questions : 

1. Define apparent specific gravity. 

2. What factors influence the apparent specific gravity of soils 

under field conditions? 

3. Does the per cent porosity vary as the apparent specific 

gravity ? 

4. From the standpoint of crop production, what is the impor- 

tance of soil porosity? 



[84] 



EXERCISE XXXVIII 
SPECIFIC HEAT OF SOILS 

Object. The object of the exercise is to determine the 
specific heat of soils. 

Materials needed. Specific-heat apparatus ; two thermom- 
eters ; three crystal dishes ; graduate (200-cc.) ; distilled 
water ; drying oven ; balance ; water-free soils. 

Procedure. 1. Fill the three crystal dishes, one with each 
type of soil, and weigh to three decimal places. 

2. Place one crystal dish, filled with soil, on the upper 
shelf of the oven. 

3. Through the opening in the top of the oven insert one 
of the thermometers, extending it down into the soil in the 
dish. 

4. Heat until the thermometer reads between 100° and 
110° C. While the soil is heating weigh the calorimeter 
cup and stirring rod and determine their water equivalent 
in calories (weight times specific heat). 

5. Measure into the calorimeter cup 200 cc. of distilled 
water and place it in the jacket. 

6. With the other thermometer determine the exact tem- 
perature of the water in the calorimeter ; immediately take 
the exact temperature of the soil in the oven. 

7. Quickly transfer the soil from the oven into the calo- 
rimeter, covering it as soon as possible. 

8. Insert the thermometer and stir for three or four min- 
utes, until a constant temperature is obtained throughout the 
mixture. 

[85] 



MANUAL OF SOIL PHYSICS 



9. Put the crystal dish back into the oven and let it stand 
there until it can be weighed to determine the exact amount 
of soil in the calorimeter. 

10. Repeat the above operation for each soil. 

Tabulation and calculation : 

1. Specific heat of calorimeter cup, 

2. Specific heat of water, 1.00. 



Kind of soil used 



Weight of calorimeter cup 

Weight of dish and water-free soil .... 

Weight of dish 

M — Weight of water-free soil 

T — Temperature of soil 

t — Temperature of water and calorimeter 
before adding soil 

C — Constant temperature of water and soil 
mixed in calorimeter 

W — Weight of water used plus water equiv- 
alent of calorimeter 

iS' — Specific heat 



Sand Surface Soil Subsoil 



Formula : 
References : 






Coleman : Elements of Physics, pp. 182-185. 
King : Physics of Agriculture, pp. 29, 215-217. 
Hall : The Soil, pp. 128-129. 
Lyon and Fippin : Soils, pp. 455-456. 
Hilgard: Soils, p. 301. 



Questions : 



1. Derive the above formula (Coleman). 

2. What is specific heat? 

3. What factors influence the specific heat of soils? 

4. Does a knowledge of the specific heat of a moist soil aid in 

determining whether it is a " late " or an " early " soil ? 

[86] 



EXERCISE XXXIX 



EVAPORATION OF WATER 

Object. The object of the exercise is to study the rate of 
evaporation from soils as compared with the evaporation from 
a free-water surface. 

Materials needed. Two evaporating pans ; surface soil ; 
balance; plotting paper. 

Procedure. Place in one of the pans a layer of surface soil 
2 inches deep and add water until the moisture content is 
about 25 per cent. Fill the second with water to a depth 
of 2 inches. The water used in both pans should be at about 
room temperature. Weigh, place in full sunlight, and note 
the loss from each by weighing every twenty minutes for 
two hours. 

Plot two curves showing the rate of evaporation from the 
two pans and tabulate your results in a form similar to the 
following : 







Grams of Water evaporated diking Each 
Ten Minutes 




1st 


2d 


3d 


4th 


5th 


6th 


7th 8th 


Total 


Free-water surface . . 
Soil surface 























References : 



Fletcher : Soils, pp. 88-89. 

Bulletin No. 188 of the United States Department of Agriculture, 
Bureau of Plant Industry, pp. 16-30. 

Twenty-fourth Annual Report of the Nebraska Agricultural Ex- 
periment Station, pp. 97-101. 

[87] 



MANUAL OF SOIL PHYSICS 

Questions : 

1. Account for the fact that evaporation from a free-water sur- 

face is slow at first and faster at the end of the period. 

2. What factors influence the rate of evaporation ? % 

3. According to the references, about how much water will be 

evaporated from the free-water surface in six months ? 

4. Compare the rate of evaporation from the soil with that 

from the leaves of plants. 



[88] 



EXERCISE XL 



MOISTURE DETERMINATIONS OF FIELD SOILS 

Object. The object of the exercise is to determine the 
moisture content of soils under field 
conditions. 

Materials needed. Two augers or 
tubes (one 6-foot and one 3-foot) ; 
eighteen tin boxes (in case) ; dry- 
ing oven ; balance. 

Procedure. 1. Weigh the tin 
boxes, being sure that each is prop- 
erly labeled. 

2. Take composite samples from 
each foot of soil to a depth of 6 
feet in an alfalfa field, a cornfield, 
and a pasture. Take notes regard- 
ing topography, vegetation, etc. 
(Care should be taken in securing 
the samples to put the covers on 
the boxes as soon as the soil is 
placed in them, to prevent loss 
from evaporation.) 

3. Weigh the samples carefully. 

4. Place the boxes in an oven 
with the lids removed, and heat at 
a temperature of 110° C. until the samples are water-free, 

5. Weigh samples again. 

[89] 




Fig. 14. Soil augers, tubes, 
and other apparatus for mak- 
ing moisture determinations 



MANUAL OF SOIL PHYSICS 

6. Compute the per cent of moisture in the samples, using 
the water-free soil as a basis. 

Record your results in a form similar to the following : 



Field. 



Date. 



Depth 


Weight 
of 
Box 


Weight of 
Box and Soil 


Loss 

IN 

Water 


Weight of 

Water-free 

Soil 


Amount of 
Water in Soil 


Feet 


Before 
heating 


After 
heating 


Per cent 


Inches of 
rainfall 




Grams 


Grams 


Grams 


Grams 


Grams 









Note. In computing the inches of rainfall, assume the soil to have an 
apparent specific gravity of 1.3. 

References : 

Lyon and Fippin : Soils, pp. 135-165. 

Twenty-fifth Annual Report of the Nebraska Agricultural Experi- 
ment Station, pp. 71-73, 106-110. 
Widtsoe : Dry-Farming, pp. 94-129. 
Hall : The Soil, pp. 64-67. 
Hopkins : Soil Fertility and Permanent Agriculture, pp. 577-583. 

Questions : 

1. Comparing the moisture content of the three fields, in 

which foot do you find the greatest variation of 
moisture ? 

2. How do you account for the fact that the three fields differ 

in moisture content? Explain. 

3. What factors influence the amount of moisture found in 

field soils? 

4. Rainfall is disposed of in what way? 

5. What practical methods may be employed which will favor 

the storing of moisture in the soil ? 



[90] 



EXERCISE XLI 

STANDARDIZATION OF THE EYEPIECE MICROMETER 

Object. The object of the exercise is to standardize the 
micrometer scale of the microscope and learn the value of 
each division. 

Materials needed. Microscope ; stage micrometer. 

Procedure. Place the micrometer scale on the microscope 
stage and, using the No. 10 eyepiece, determine for each 
of the objectives the number of divisions or spaces of the 
eyepiece micrometer that correspond to 1, 0.5, 0.1, 0.05, and 
0.005 mm. of the stage micrometer. 

Tabulate in a form similar to the following the number of 
spaces of the eyepiece micrometer that correspond to the size 
of the various classes of soil particles. 



Microscopk No. 



Soil Class 


Diameter in 


Number of Spaces 


Nitmber or Spaces 


Millimeters 


in 16mm. Objective 


in 4 mm. Objective 


Coarse sand 


1.0 to 0.5 






Medium sand 


0.5 to 0.25 






Fine sand 


0.25 to 0.1 






Very fine sand 


0.1 to 0.05 






Silt 


0.05 to 0.005 






Clay 


0.005 and less 







[91] 



EXERCISE XLII 
MECHANICAL ANALYSIS OF SOILS 

Object. The object of the exercise is to make a partial 
mechanical analysis of and to become acquainted with the 
texture of various soils. 

Materials needed. Microscope (standardized) ; four beakers; 
burner ; evaporating dish ; crucibles ; sieves ; pipette ; wash 
bottle ; balance ; mortar and pestle (rubber-tipped) : soils. 

Procedure. Read the entire exercise very carefully before 
attempting to work it. In making a mechanical analysis of 
soils it is very important that all composite or crumb struc- 
tures be destroyed and that the entire sample be in a single- 
grain condition. This is accomplished by gently rubbing the 
sample of soil in a mortar with a rubber-tipped pestle. In 
rubbing there should be just enough pressure to detach 
adhering particles — not enough to break them. Add just 
enough water to make the soil into a pasty mass, and pestle 
for a little while. Fill the mortar about half full of water 
and allow to settle about live minutes, or until all particles 
larger than 0.05 mm. have settled; then pour into a beaker 
the water which contains only silt and clay. Again pestle 
the soil particles for a time, add water, and allow to settle, 
again pouring off the silt and clay into the beaker which 
already contains some silt and clay particles. Continue this 
operation until all the particles are completely disintegrated. 
When disintegration is complete, the particles show sharp out- 
lines under the microscope and are glassy in appearance. 

[93] 



MANUAL OF SOIL PHYSICS 

When disintegration is complete, transfer all the soil to the 
beaker already containing silt and clay and probably some 
sand. For convenience this beaker is called A. Fill the 
beaker A with water and stir thoroughly. Allow the parti- 
cles to settle until an examination with the microscope shows 
that all particles larger than 0.05 mm. have settled ; then 
pour the turbid liquid into a second beaker B. Examine the 
sediment in the bottom of beaker B, to make sure that no par- 
ticles larger than 0.05 mm. have been poured off. In case 
sand particles have been poured off, stir the contents of beaker 
B and allow all the sand particles to settle, pouring the 
liquid containing silt and clay into a third beaker C. Return 
the sand in beaker B to beaker A. Examine the sediment in 
beaker C, and if no sand particles are found, the liquid may be 
discarded. Again fill beaker A with water and stir. As soon 
as all the sand particles have settled, pour the turbid liquid 
into beaker B. In the same manner as above examine the 
sediment in beaker B, returning any sand particles to beaker 
A. Continue this process until all silt and clay particles have 
been removed from beaker A and it contains only sand or 
particles larger than 0.05 mm. in diameter. 

Transfer the contents of beaker A to an evaporating dish 
and evaporate to dryness ; then weigh. After weighing, trans- 
fer the particles to the sieves and shake until a thorough 
separation has been made. Place each separate in a weighed 
crucible and ignite to burn off the organic matter, then weigh 
and determine the exact weight of each. 

By means of a separate sample of the original soil deter- 
mine the per cent of volatile matter that it contains (Exer- 
cise XVIII). To determine the combined weight of silt and 
clay which the sample contained, add the weights of all the 
separates and the volatile matter, and substract from the 
weight of the original sample. (A complete mechanical 
analysis may be made by separating the silt from the clay, 

[94] 



MECHANICAL ANALYSIS OF SOILS 

using the materials that are discarded in the separation of 
the sand and gravel classes.) In order to obtain a check on 
the amounts of particles lost, analyze all samples in duplicate. 

By the above method determine the per cent (water-free 
basis) of coarse gravel, fine gravel, coarse sand, medium sand, 
fine sand, very fine sand, silt, and clay, together with the 
per cent of organic matter, in the samples given out at the 
storeroom. 

Tabulate your results in a suitable form, and report as soon 
as the separation is completed. 

References : 

Bulletin No. 4 of the United States Department of Agriculture, 

Bureau of Soils. 
Bulletin No. 24 of the United States Department of Agriculture, 

Bureau of Soils. 

Questions : 

1. Name five methods of mechanical analysis. 

2. Discuss briefly the force or forces used in each of the 

above methods. 



[95] 



EXERCISE XLIII 

SOIL EXAMINATION 

Object. The object of the exercise is to give practice in 
estimating approximately the texture and physical composition 
of soils. 

Materials needed. Graduate ; soil samples. 

Procedure. Procure samples of soil from the storeroom and 
study them according to the following outline: 

Dry soil 

Color 

Pulverent, crumbly, or cloddy 
Moist soil 

Color 

Floury, mealy, or gritty 

Pliable or plastic 
Composition (estimated) 

Supply of carbonates 

Organic matter (per cent) 

Gravel (per cent) 

Coarse and medium sand (per cent) 

Fine sand (per cent) 

Very fine sand (per cent) 

Silt and clay (per cent) 

Do the work rapidly, using only a few pieces of apparatus. 
In estimating the physical composition of a soil a graduate is 
sometimes of considerable help. Place 10 cc. of the soil in 
the graduated cylinder with from 60 to 80 cc. of water; shake 
and allow to settle. The amount of sand may be read very 

[97] 



MANUAL OF SOIL PHYSICS 

roughly after the soil has settled. The cylinder is of little 
aid in studying a heavy type of soil. 

In testing for carbonates place several drops of hydrochloric 
acid on a small portion of the sample. In case the soil con- 
tains about normal amounts, effervescence will not be readily 
observed ; large amounts will be easily detected. 



[98] 



EXERCISE XLIV 

EXAMINATION OF SOIL SAMPLES 

Object. The object of the exercise is to study samples of 
soil taken from the student's home farm, or some place of 
interest, in order to become more familiar with them. 

Materials needed. Samples of soil (first, second, and third 
foot of each type) ; apparatus necessary for the exercises named 
below. 

Procedure. Study each type of soil that has been procured, 
using 1 the following exercises as an outline : 

Exercise IV, Soil Classification (Origin). 
Exercise XVIII, Loss on Ignition. 
Exercise XIX, Soil Acidity and Basicity. 
Exercise XX, Determination of Humus. 
Exercise XLII, Mechanical Analysis of Soils. 
Exercise XLIII, Soil Examination. 

Tabulate your results in a suitable form. 



[99] 



WEIGHTS AND MEASURES 

1 kilogram = 2.2 pounds avoirdupois. 

1 liter = 1.056 quarts. 

1 inch = "J.").:!!)!) millimeters. 

1 pound 153.59 grams. 

1 cubic fool "t' water weighs approximately 62.5 pounds. 

1 inch of water over 1 Bquare fool weighs approximately 5.2 pounds. 

1 acre inch of water = 113.3475 tons. 

1 acre 13560 square feet. 

1 acre foot contains 4-3560 cubic feet. 

2 7T/- or ttD — circumference of circle. 
irr- — area of circle. 

I m 3 or 7r/>- = area of Bphere. 

\/'-\ 7n -:t or I/O 7r/> :! = volume of sphere. 

■nr-h = volume of cylinder (h = altitude). 



[101] 



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